Deck 10: Inductance

Question 1

When a switch is closed, completing an LR series circuit, the time needed for the current to reach one half its maximum value is ____ time constants.

A)0.250
B)0.500
C)0.693
D)1.00
E)1.44

Answer 1

0.693

Question 2

Find the magnetic energy stored in the air gap between two very large magnetic pole pieces, one North, one South, each with an area of 100 cm2.Assume the 0.05 T magnetic field is uniform within the 2-cm gap.

Answer 2

0.2 J

Question 3

For the circuit shown, what is the rate of change of the current in the inductor when the current in the battery is 0.50 A?

A)600 A/s
B)400 A/s
C)200 A/s
D)800 A/s
E)500 A/s

Answer 3

200 A/s

Question 4

Before the switch is closed in the figure, the potential across the capacitor is 200 V.At some instant after the switch is closed, the instantaneous current is 0.70 A.What is the energy in the capacitor at this instant?

A)49 mJ
B)31 mJ
C)80 mJ
D)0.13 J
E)62 mJ

Question 5

The switch in the figure is closed at t = 0 when the current I is zero.When I = 15 mA, what is the potential difference across the inductor?

A)240 V
B)60 V
C)0
D)180 V
E)190 V

Question 6

A circuit contains two inductors of 6.0 mH inductance in series placed in parallel with an inductor of 8.0 mH inductance.After one of the 6.0 mH inductors burns out, the repair person wants to replace all three inductors with one inductor of equivalent inductance.Assuming inductors combine in series and parallel the same way resistors do, what inductance should she use?

A)3.0 mH
B)3.4 mH
C)4.8 mH
D)11 mH
E)20 mH

Question 7

When a switch is closed, completing an LR series circuit, the time needed for the current to reach three-quarters its maximum value is ____ time constants.

A)0.500
B)0.693
C)0.725
D)1.33
E)1.39

Question 8

The magnetic field in a superconducting solenoid is 3.0 T.How much energy per unit volume is stored in the solenoid, in J/m3? $\mu$ 0 = 4 $\pi$ *10-07 T .A/m

Question 9

There is no current in the circuit shown in the figure below until the switch is closed.The current through the 20- $\Omega$ resistor the instant after the switch is closed is either [1] 15 A or [2] 5.0 A, and the current through the 20- $\Omega$ resistor after the switch has been closed a long time is either [3] 5.0 A or [4] 15 A.Which combination of the above choices is correct?

A)[1] and [3]
B)[1] and [4]
C)[2] and [3]
D)[2] and [4]
E)None of these

Question 10

What is the inductance of a series RL circuit in which R = 1.0 K $\Omega$ if the current increases to one-third of its final value in 30 $\mu$ s?

A)74 mH
B)99 mH
C)49 mH
D)62 mH
E)none of the above

Question 11

When a switch is closed to complete a DC series RL circuit:

A)the electric field in the wires increases to a maximum value.
B)the magnetic field outside the wires increases to a maximum value.
C)the rate of change of the electric and magnetic fields is greatest at the instant when the switch is closed.
D)all of the above are true.
E)only (a) and (c) above are true.

Question 12

The figure shows an LR circuit with a switch and a 240-volt battery.At the instant the switch is closed the current in the circuit and the potential difference between points a and b, Vab, are:

A)0 A, 0 V
B)0 A, -240 V
C)0 A, +240 V
D)0.024 A, 0 V
E)0.024 A, +240 V

Question 13

Which of the following are the units of a henry and a farad respectively?

A)J . s2/C2 and C2/J
B)V . s/A and V/C
C)V/(A . s) and C/V
D)N .m/A2 and 1/J
E)None of the above

Question 14

A series LC circuit contains a 100 mH inductor, a 36.0 mF capacitor and a 12 V battery.The frequency of the electromagnetic oscillations in the circuit is:

A)5.73 *-4 Hz.
B)9.55 * 10-3 Hz.
C)0.442 Hz.
D)2.65 Hz.
E)44.0 Hz.

Question 15

A series LC circuit contains a 100 mH inductor, a 36.0 mF capacitor and a 12 V battery.The period of the electromagnetic oscillations in the circuit is:

A)0.0227 s.
B)0.377 s.
C)2.26 s.
D)105 s.
E)1750 s.

Question 16

After a switch is thrown to remove the battery from a DC LR circuit, but the circuit is still left complete, the time constant represents:

A)the time rate of change of the current in the circuit.
B)the time rate of change of the induced emf in the circuit.
C)the magnitude of the ratio of the current to the time rate of change of the current.
D)all of the above.
E)only (a) and (b) above.

Question 17

A series LC circuit contains a 100 mH inductor, a 36.0 mF capacitor and a 12 V battery.The angular frequency of the electromagnetic oscillations in the circuit is:

A)36.0 * 10-4 rad/s.
B)6.00 * 10-2 rad/s.
C)2.78 rad/s.
D)16.7 rad/s.
E)277 rad/s.

Question 18

A circuit contains two inductors of 6.0 mH inductance in parallel placed in series with an inductor of 8.0 mH inductance.After one of the 6.0 mH inductors burns out, the repairman wants to replace all three inductors with one inductor of equivalent inductance.Assuming inductors combine in series and parallel the same way resistors do, what inductance should he use?

A)3.0 mH
B)3.4 mH
C)4.8 mH
D)11 mH
E)20 mH

Question 19

An inductor produces a back emf in a DC series RL circuit when a switch connecting the battery to the circuit is closed.We can explain this by:

A)Lenz's law.
B)increasing magnetic flux within the coils of the inductor.
C)increasing current in the coils of the inductor.
D)all of the above.
E)only (a) and (c) above.

Question 20

Coaxial Cable A has twice the length, twice the radius of the inner solid conductor, and twice the radius of the outer cylindrical conducting shell of coaxial Cable B.What is the ratio of the inductance of Cable A to that of Cable B?

A)
B)
C)2
D)
E)

Question 21

An RLC circuit has L = 250 mH, C = 0.200 $\mu$ F, and R = 2.00 k $\Omega$ .What is the angular frequency of its damped oscillations?

Question 22

A 10-mH inductor is connected in series with a 10-ohm resistor, a switch and a 6-volt battery.What is the time constant of the circuit? How long after the switch is closed will the current reach 99 per cent of its final value?

Question 23

If we wished to construct a 'tank circuit' where electric charge originally stored on a capacitor flows through an inductor, then back again, what value of inductance should we place in series with a fully-charged 100 $\mu$ 0F capacitor to get the circuit to resonate at 60.0 Hz?